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參數(shù)資料
| 型號： | AN874 |
| 廠商： | Maxim Integrated Products, Inc. |
| 英文描述： | Using the MAX6950 and the MAX6951 LED Display Drivers with Multiplex Dual-Digit Displays |
| 中文描述： | 使用與多重雙位數(shù)字顯示MAX6950可與MAX6951 LED顯示驅動器 |
| 文件頁數(shù)： | 1/3頁 |
| 文件大?。?/td> | 47K |
| 代理商： | AN874 |
APPLICATION NOTE
HIGH FREQUENCIES DAMPER DIODES
AN874/0996 Ed : 2
B. RIVET
INTRODUCTION
The trend in new monitors is for ever increasing
switching frequencies of the horizontal deflection
stage : 64kHz ---> 110kHz.
SGS THOMSON has developed new 1500V
Damper diodes (DTV64D-DTV82D-DTV110D)
using a new silicon structure and a suitable lifetime
reduction process both optimized in order to
reduce the peak forward voltage (V
FP
) .
For
high
switching
parameters optimization of the damper diodes
becomes more and more critical. This application
note describes these key parameters and the
associated power losses.
frequencies,
the
key
KEY PARAMETERS OF THE DAMPER DIODE
The key parameters of a damper diode are the
peak forward voltage (V
FP
), the forward voltage
(V
F
) and the recovery time (trr).
Reverse recovery time : trr
The table in fig.1 gives the maximum reverse
recovery time for the three high frequency damper
diodes.
The application note "CHOICE OF DAMPER
DIODE FOR A HORIZONTAL DEFLECTION"
explains in detail the very particular mechanism of
the switching OFF losses (Poff) in the damper
diode. The maximum value of trr has been chosen
to be sure that the switching OFF losses in the
damper diode will be negligible.
Voltage drop : V
F
This parameter fixes the value of the conduction
losses (Pcond) in the diode. This losses can be
estimated by :
Pcond
=
VtoIp
2
δ
=
RdIp
2
3
δ
Where :
Ip
δ
Vto : Threshold voltage of the damper diode
Rd
: dynamical resistance of the
damper diod
e
: peak current in the diode
: duty cycle of the conduction time
Example : With a DTV64D
Vto (typ.) = 0.89V
Rd
(typ.) = 35m
and
Ip = 6A
δ
= 0.45
We find
Pcond =1.4W
Peak forward voltage : V
FP
This parameter has to be as low as possible in
order to reduce switching ON losses in the diode.
The peak forward voltage depends mainly on the
dIF/dt. (V
FP
increases with dIF/dt). For this
application the d
IF
/dt is typically equal to 60A/
μ
s.
Fig.2 shows the current and voltage across the
diode when it turns on, in the following conditions :
Ip = 6A d
IF
/dt = 60A/
μ
s Tj = 100°C with DTV64D,
DTV82D and DTV110D.
trr max
I
F
=1A - d
IF
/dt =50 A/
μ
s
V
R
= 30V - Tj = 25°C
DTV64D
135 ns
DTV82D
125 ns
DTV110D
115 ns
Fig.1
: Maximum reverse recovery time of
DTV64D, DTV82D and DTV110D.
1/3
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